CHAPTER XII 



THE ASCENT OF SAP 



'T^HE water from the mains, down under the 

 -'- streets, goes up through standing pipes to 

 places where it is wanted in the top stories of tall 

 buildings. 



The water which the root-hairs take in from the 

 soil is upward-bound also. This water finds no 

 pipes ready to carry It up and on through roots, 

 trunk, and branches — but it makes the journey 

 nothwithstanding. 



The microscope shows that the root-tip Is like 

 a honeycomb — all made of cells. So, indeed, is 

 every part of a tree — Its wood, its leaves, its 

 flowers. Its fruit, its seed (Fig. 32). 



The root-hair Is one narrow cell, or tube, and a 

 very thin wall separates its upper end from the 

 cell just beside it (see Fig. 30). This second cell 

 is full of sap, in which so many things are dis- 

 solved that it Is much denser than the earth-water 

 in the root-hairs. The cell wall — like many 

 other membranes in animal and plant bodies — is 

 so made that gases or liquids can pass gradually 

 through It. 



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